Telephone system



Nev. 15, 1938. GJV. KING TELEPHONE SYSTEM 11 Sheets-Sheet 1 Filed June21, 1935 65E amt 9mm 5%. 3E nut v 95 95 Not GR Q Um INVENTOR c.- v. mwa@m A T TOR/V5 V Nov. 15, 1938. G v Km 2,136,620

TELEPHONE SYSTEM Filed June 21. 1935 ll Shaets-Sheec 2 lNl ENTOR G. V.KING am A ATTORNE V Nov. 15, 1938 FIG. 3

SECOND L/NK G. V: KING TELEPHONE SYSTEM 'Filed June 21, 1935 11Sheets-Sheet 3 F /F TH LINK FIRST LINK INVENTOP By G. 1 K/NG ATTORNEYNov. 15, 1938. G. v. KING TELEPHONE SYSTEM Filed June 21, 1935 llSheets-Sheet 4 Q g /NVENTOR (I. 1 KING ATTORNEY G. V. KING Nov. 15,1938.

TELEPHONE SYSTEM 11 Stieets-Sheet 5 Filed June 21, 1935 mNm QQmINVENTOF? G. 1/. KING @gm ATTORNEY Nov. 15,1938. G. v. KING 2,136,620

TELEPHONE SYSTEM Filed June 21. 1935 ll Sheets-Sheet 6 //V VE N 0/? a.V. KING A TTOR/VE) G. V. KING Nov. 15, 193.

TELEPHONE SYSTEM Filed June 21, 1935 ll Sheets-Sheet 7 ATTORNEY Nov. 15,1938. v K 2,136,620

TELEPHONE SYSTEM Filed June 21, 1935 ll Sheets-Sheet 8 55mm LINK.

S/XTHLINK lNl/EN 8V 6. 1 KING A TTORNE V Nov. 15, 1938. G v, KING2,136,620

TELEPHONE SYSTEM Filed June 2l, 1935 11 Sheets-sheaf, 9

INVENTOR G. l/. KING BY waeem'w ATTORNEY Nov. 15, 1938. G. v. KING2,136,520

TELEPHONE SYSTEM Filed June 21, 1935 ll Sheets-Sheet 10 NW9 h P 1 A 7'TORNE V Nov. 15, 1938. a. v. KING TELEPHONE SYSTEM Filed Jun 21, 1955 llSheets-Sheet ll W3 xvi INVENTOR By a. l K/ NG 696M A T TOR/V5 V PatentedNov. 15, 1938 PATENT OFFICE TELEPHONE SYSTEM Gerald V. King, Chatham,'N.J., assignor to Bell Telephone Laboratories Incorporated, New York, N.Y., a corporation of New York Application June 21,

9 Claims.

This invention relates to telephone systems and particularly to systemsinvolving the use of automatic equipment for establishing conversationalconnections.

The object of the invention is to improve small automatic telephonesystems, such as satellite systems, by performing the various local andinteroffice switching connections with a unitary and compact arrangementof switch structure and circuits.

A feature of the invention is the use of a crossbar switch unit pergroup of local lines which combines in a ingle structure the functionsof a line finder and a connector in relation to a group of links commonto all switching units. Each switch unit is provided with horizontalline contacts and vertical link contacts coordinated in relation to eachother into one cross-point Whereby the operation of one horizontal andone vertical magnet in the proper combination closes said contacts orcross-point of a calling line through an allotted link, and theoperation of another horizontal and vertical magnet in propercombination closes the defining cross-point of the called line oroutgoing trunk through said allotted link. All the lines in eachswitching unit are accessible to one end of all the common links whencalling and all the lines and trunks are accessible to the other end ofsaid links when said lines or trunks are called.

Another feature of the invention resides in the allocation of aplurality of cross-points on one or more of said switch units for theuse of outgoing trunks which may extend to a main central office andwhich may be reached by a calling subscriber by dialing a predetermineddigit which serves to extend his connection to the trunk cross-pointlevel and to the operated cross-points of an idle trunk in that level.

The nature of the invention will be more clearly understood from thefollowing description of one embodiment thereof and of possiblemodifications thereto with reference to the accompanying drawings inwhich;

Figs. 1 to 10, inclusive, when arranged as shown in Fig. 13, disclose anumber of link circuits accessible to groups of subscribers lines andtrunks shown in Figs. 2 and 6 for the purpose of completing connectionsbetween said lines or between said lines and trunks;

Fig. 11, arranged below Fig. 10, as shown in Fig. 13, is the timing,ringing and alarm circuit which serves all links;

Fig. 12 is a diagrammatic presentation of the 1935, Serial No. 27,675

arrangement between lines, links, and switching units contemplated bythe invention.

Before discussing the details of operation, attention is directed toFig. 12. In this layout of three cross-bar switching units, identifiedas frames 1, 2 and 3, twenty lines are shown, ten on frame 1 and ten onframe 2. Ordinarily, each frame iscapable of holding five links, each ofwhich can be connected to any two lines on different horizontal levelsthrough the appropriate cross-points. pacity of the exchange is greaterthan ten lines, say twenty lines, and the traflic originating from saidlines does not warrant the use of more than five links, the additionalten lines can be located on a second frame, as for instance on frame 2,and the five links accessible to frame 1 can be extended so as to beavailable to the additional ten lines on frame 2. In this manner, thenumber of lines which can be included in one exchange unit limited tofive links can be extended, in groups of ten, almost indefinitely,although the circuits of the present invention, being designed primarilyfor application in rural districts, limits the total number of lines toa maximum of fifty lines, that is five switching units of ten lineseach. Moreover, while the number of lines can be increased with respectto a definite number of links, conversely, my invention makes itpossible to increase the number of links with respect to a definitenumber of lines. If, for instance, the quantity of trafiic whichoriginates in an exchange of twenty lines is greater than that which canbe handled successfully by five links and two additional links areneeded, said links may be accommodated on a separate or third switchingunit to one half of whose horizontal cross-points may be multipled thelines from the first switching unit and to the other half the lines fromthe second switching" unit with the two links extendingto both halves ofthe third switching unit. In Fig. 12, an exchange of twenty lines isillustrated as needing seven links to handle the trafiic successfully.Consequently a third switching .unit is supplied, frame 3, to the lefthalf of whose horizontal cross-points the lines appearing on frame 1 areextended and to the right half of whose horizontal cross-points thelines appearing on frame 2 are extended and the two additional links,namely, links 6 and 7 are extended to both halves of frame 3. Obviously,if ten links were needed to serve the twenty lines, then a fourthswitching unit would be required and the third and fourth switchingunits could be arranged so that the lines appearing on frame 1 would ex-On the other hand, if the catend clear across frame 3 and the linesappearing on frame 2 would extend clear across frame 4 with the fiveadditional links accessible to each of the twenty lines through frames 3and 4.

Inasmuch as the preferred embodiment of this invention is disclosed withrespect to its application to a rural telephone system in which aplurality of telephone stations may be located in the same pair of lineconductors, as for instance, five stations on the tip and five stationson the ring, and which makes it necessary to provide code ringing toidentify each station and to make it possible for one station to callanother station on the same line, the more detailed description of thisinvention will include the operations required to establish a connectionbetween a station on one line and a station on another line, aconnection between two stations on the same line and (3) a connectionbetween a station and an outgoing trunk, three of which occupy the firstthree horizontal cross-points, respectively, on frame 1 and the lefthalf of frame 3.

It must be understood, however, that the invention herein set forth andclaimed is not limited to any such arrangement but can be readilyapplied by any one skilled in the art to an exchange having individuallines or to any other arrangement of lines and stations that suggestthemselves by the character of the service to be rendered as, forinstance, two or four party line service or single party service.

When any one of the group of subscribers in the group shown in Fig. 6,say subscriber 624, initiates a call, line relay B is operated over acircuit extending from grounded battery through the left winding of saidrelay, outer contacts of cut-off relay 60I, the subscribers line loop,inner contacts of relay 60I, right winding of relay 600 to ground. Relay600 operates and completes a circuit for selective magnet 2I2 whichextends from ground through the contacts of relay 600, left backcontacts of relay 602, conductor 633, upper No. 4 contact-set of relay206, conductor 2I4, right winding of selective magnet 2I2, conductor2I5, lower normal contacts of relay 20B, conductor 2I6, left contacts ofrelay I02, right outer contacts of relay I03, right contacts of relayIOI, to battery and ground. Magnet 2I2 operates and locks in a circuitcompleted from operating ground as traced to its left winding, throughits left front contacts, left back contacts of selective magnets 2II,2I0 and 209, conductor 2", winding of relay I02, right inner contacts ofrelay I03, right contacts of relay IN, to battery and ground. Relay I02operates in the locking circuit of magnet 2I2, closes an obvious circuitfor slow-operate relay I04 over its right front contacts and opens theoperating circuit of magnet 2I2 at its left contacts.

In the usual construction of the cross-bar switch, the so-called 100point switch preferably has one selecting magnet for ten horizontalcross-points, thus making it possible to provide five links to theframe, each link having one calling cross-point and one calledcrosspoint; that is, one set of contacts through which the link gainsaccess to the calling line and another set of contacts through which itgains access to the called line. However, where the link capacity isgreater than five, and other switch frames have to be provided toaccommodate additional links, the number of frames is, of course,determined by the number of links. Where, as in the case beingillustrated according to Fig. 1

seven links are provided for twenty lines, an additional frame (frame 3)is split in two and the two additional links accommodated thereon asalready described. Under such circumstances, when a subscriber, such assubscriber 624, initiates a call and the selecting magnet 2I2, on themain frame for the horizontal level of the calling line is operated, italso becomes necessary to operate the selecting magnet for the samelevel on the additional frame since the idle link to be selected andattached to the calling line may be either in the main frame or theauxiliary frame. In the drawings, Fig. 4 represents the auxiliary frame,while its selecting magnets 306 to 3I0 are shown on Fig. 3 and of whichselecting magnet 309controls the continuation, on the auxiliary frame,of the level controlled by selecting magnet 2I2 on the main frame.Consequently when relay I04 operates, it completes a circuit whichextends from ground through its contacts, conductor I06, conductor GITright contacts of magnet 2I2, conductor 2I8, right winding of selectivemagnet 309 to battery and ground. Magnet 309 operates and then extendsits operating ground through its right contacts, conductor 3II, topouter contacts of relay 208, winding of relay 2I9 to battery and ground.Relay 2I9 operates and completes a circuit for relay I008, which circuitextends from ground on the left contacts of relay 2I9, conductor 224,left normal contacts of link make-busy key III, left back contacts ofrelay H0 (if the first link is idle), conductor H2, No. 8 contact-set ofrelay I0I5 winding of relay I008, to battery and ground. Relay I008operates and, through its right sets of contacts, connects ground toconductors 3I2 and 3I3 respectively, the former of which extends to theoperating winding of the holding magnet 300 on the crossbar frame 1while the latter extends to the operating winding of the holding magnet100 on the lower cross-bar frame 2. Inasmuch as the calling line 624appears in the upper frame and the origination of the call therefrom hasresulted in the operation of relay 2 I9, the circuit of holding magnet300 of the first link, if idle, is completed over conductor 3| 2,winding of magnet 300 conductor 320, right contacts of relay' 2I9 tobattery and ground. Magnet 300 operates, looks from battery through itslower winding and contacts, conductor 3I5, right back contact of relayIOI0, conductor IOI6 to ground over the No. 2 contacts of relay IOI5and, since horizontal selecting magnet 2I2 is also operated, thecombination of the operated selecting magnet 2I2 and the operatedholding magnet 300 serves to operate contact-set 3| 4 on the first linkand thereby extend conductors 609, SH and (H2 of the calling line 624 tothe first link. As soon as cross-point 3I4 is operated, then, by virtueof succeeding operations in the link which result in the operation ofrelay I0I5 as described hereinafter, a circuit is completed for relay602 which extends from ground and battery, through the right winding ofsaid relay, conductor 6I2, third set of contacts on cross-point 3I4,conductor IOI6, to ground on the No. 2 contact-set of relay I0I5 Relay602 operates and performs functions described hereinafter.

If the calling line had been located on frame 2, and in thecorresponding fourth horizontal position on the frame as line 624 islocated on frame 1, say line 634 (not shown), with its extension to thefourth horizontal position on the right of frame 3, then after theoperation of the proper selecting magnet on frame 2, instead of closingthe circuit of holding magnet 300 the circuit of holding magnet I00 onframe 2 would have been completed from ground and battery through theright contacts of relay 606, conductor 628, upper winding of holdingmagnet T60 conductor 3 I3, right inner contacts of relay H108 to ground.In this way, only the holding magnet of the chosen link in the frame inwhich the calling line belongs is operated.

Before proceeding with the further operations which follow theconnection of a link to the calling line, it is necessary to observethose circuit operations which, prior to this connection, take place toinsure that, in the event that more than one line calls at the sametime, links, if available, are connected to each of said lines in adefinite order of preference and only after each link has beenconnected; to a line.

Suppose that subscriber 624, whose line according to Fig. 12, is locatedon cross-bar frame 1 and on the fourth level thereof and that subscriber63L whose line appears on cross-bar frame 2 and on the first levelthereof, simultaneously initiate calls by removing their respectivereceivers off their hooks, line 624 will cause the operation of linerelay 600 as already described while line 63H will cause the operationof line relay fiIZ by the closure of an obvious circuit similar to thatfor line relay 600.

It will be recalled that the operation of relay 690 resulted in theoperation of horizontal selecting magnets H2 and 309 controlling thosecross-points on the link frames to which the line I524 is extended. In asimilar manner, the operation of relay EH2 causes the operation ofhorizontal selecting magnets 601 and 306 of those cross-points in thelink frames to which line 63I extends. Accordingly, when relay 6I2operates, a circuit is completed which extends from. ground on thecontacts of relay BI2, left normal contacts of relay 6M, conductor BIS,No. I contact set of relay 603, right winding of selective magnet 60?,left normal contacts of relay 605, conductor EIE, conductor 2I6, leftcontacts of relay I02, right outer contacts of relay I03, right contactsof relay IilI, to battery and ground. It will be recalled that thecircuit of horizontal selecting magnet 2 I2 was similarly completed toconductor 2m and thence to battery and ground on the back contacts ofrelay IOI. Assuming that the circuit of each of the selective magnets2I2 and till is closed simultaneously then, when. magnet 60'! operates,a circuit path is partially completed for selective magnet 306 whichextends from ground and battery through its left winding, conductor 3I1, right contacts'of magnet 601, conductor GI'I, conductor Illfi, tothe contact of relay I64. However, each of the selecting magnets 2I2 andGill, on operating, closes a locking path through their respective leftwindings and front contacts, the left back contacts of the selectingmagnet immediately ahead of them in preference, to conductor 2|! andthence to battery and ground on the back contacts of relay IOI throughthe winding of relay I02. Inasmuch as the operation'of magnet 212, whichis ahead of magnet 5431, by opening its back contacts breaks the lockingpath of magnet 691, only magnet 2I2 whose locking path is not broken,can lock. Hence, when relay I02 operates as before described, theoperating circuit of magnets 60'! and 2I2 is opened at its back contactsand since magnet 2 I2 is now locked and magnet 60] is not, magnet Billreleases and further opens the previously described path for magnet 306.In virtue of the operations already described, the first link, if idle,becomes attached, therefore, to line 624.

Should the first link be busy, this condition causes the mechanicallocking of relay H0 in the manner described hereinafter, and the groundconnected to conductor 224 is advanced over the left front contact ofrelay H0 back contact of relay H0 of the second link, if idle, the No. 8contact-set of relay I0I5 of said link, to the winding of the startrelay corresponding to relay I003 in said second link. Further, if thesecond link is also busy and, therefore, relay H0 is mechanically lockedin an operated position, the ground on conductor 224 is advanced overthe left front contact of relay H0 to the armature of relay "H0 (notshown) in the third link and from thence either over the back contact ofthis relay, if the link is idle or over the front contact if the link isbusy, to the contacts of relay H0 (not shown) of the fourth link; thecircuit path being extended over an operated relay H0 in each busy linkuntil an idle one is found, after which operations will take placesimilar to those already described. Should all links be busy at the timea subscriber initiates a call, relay H0 in each link will be locked inan operated position, whereupon a circuit is completed which extendsfrom ground on the right front contacts of each relay I'Iil up to andincluding relay H0 of the seventh link, conductor I, winding of relayN16, to ground and battery. Relay I00 operates and closes an obviouscircuit for relay IOI which operates and opens the battery connection tothe operating circuits of the horizontal selecting magnets, thus makingit impossible to operate any of them if no link is available. Relay IOIfurther completes a circuit which extends from ground through its leftcontacts, conductor I07, winding of magnets 109 -109 in parallel, tobattery and ground. Each of these magnets operates and unlocks itscompanion relay 1 I 0 409 So long as each of the links is busy, then,inasmuch as relay I008 in each of said links releases immediately afterthe horizontal selecting magnets are operated, as more completelydescribed hereinafter, each of the separate make-busy relays HU -Hi1will remain operated over a path which, for relay H0 extends from groundand battery through its right winding, conductor I08, left contacts ofrelay I006, No. 2 contact-set of relay M5 to ground; relay I0I5 in eachof the busy links having been operated as described hereinafter. linkbecomes idle, relay I0I5 releases, the corresponding make-busy relay II0 releases and the link is made available for service. Also, when a linkbecomes idle and its make-busy relay H0 releases, the circuit of relayI06 is broken, causing the release of relay ml, the consequent releaseof all locking magnets 'IEl9 'I09 and the restoration of battery to thestart circuit of the horizontal selecting magnets.

Returning, now, to the allotment of an idle link to the subscriber online 63I on the assumption that said subscriber has started the call atthe same time as the subscriber on line 624, and assuming that, due tothe preferential arrangement of line 624 ahead of line 63 I, a link hasbeen connected to line 624, it will be recalled that the: horizontalselecting magnets 601 and 306, corresponding to the position of line 63Ion the link frames, could not remain operated once the locking circuitof magnet Bill was opened by the operation of magnet 3I2. However, assoon as the link is allotted to line 624 and relay 602 has On the otherhand, as soon as a operated, cut-01f relay I operates over a circuitcompleted through the right locking contact of relay 602 to a previouslytraced ground on conductor GIZ, whereupon line relay 600 releases andopens the locking circuit of horizontal selecting magnet 2I2 the releaseof which, in turn, opens the locking circuit of the correspondingselecting magnet 309 on the third link frame. Once the locking circuitof the horizontal magnet 2I2 is opened, relay I02 releases and restoresthe operating and locking battery for all of the horizontal selectingmagnets. The horizontal magnet 60? and also consequently, horizontalmagnet 306 can now operate and lock and cause the allotment of an idlelink to line 63L Having shown how each one of two idle links may beconnected to each one of two calling lines on which calls are initiatedsimultaneously, the operations which follow the connection of the firstlink to a line on which a subscrihers station, say station 624, islocated, will now be described. It will be assumed that the subscriber624 wishes to establish a connection with another subscribers station,say station 63I whose line, according to Fig. 12, is located on thefirst horizontal level of frame 2 and that, in order to establish saidconnection, subscriber 624 dials the number 319. The first two digits ofthis number identify the position of the line on the frame on which itis located while the last digit identifies the ringing code assigned tostation 63L When the cross-point 3I4 is closed, a circuit is completedfor relays IOI2, IOI3 and IOI4 over the line loop which may be tracedfrom ground and battery through the winding of relay IOI2, bottom outerback contacts of relay IO0I, bottom outer contacts of relay I000,conductor IOIl, second contact from the top of cross-point 3I4,conductor 6II, loop of subscribers line 024, conductor 609, top contactof cross-point 3, conductor 3I6, top outer back contacts of relay I000,top outer contacts of relay IO0I, winding of relay IOI3, conductor IOI8,left normal contacts of relay III I, left normal contacts of relay 906,conductor 9I5, left winding of transformer I I3I to ground. Relays IOI2and IOI3 operate closing obvious parallel circuits to the winding ofrelay i0 which operates. Relay IOI4 causes the operation of relay I0I5which, on operating connects: (1) ground through its No. I contact-setto conductor IOI9 which extends to the No. I contact-set of relay I0I5of the second link and from thence through corresponding contact sets ofrelay I0I5 -I0I5 of all'the seven links, from the last relay of which,that is relay I0I5 it extends by way of conductor 800, to the winding ofregister I which, on the other side of its winding, is connected tobattery and ground. If, when the first link is taken into use, asabovedescribed, and relay I 0 I 5 operates, the remaining six links arebusy, each of their corresponding relays IOI5 is operated and thecircuit to register I 05. is completed to indicate an all-busy conditionof the links; (2) through its No. 2 contact-set,

- relay I0I5 connects ground to conductor IOI6 which completespreviously described circuits to the right winding of relay 602 and tothe locking winding of holding magnet 300 (3) over its No. 3 contact-setrelay I0IIi extends ground through the bottom inner back contacts ofrelay IBIH and thence to the No. 4 contact of relay i009; (4) over itsNo. 4 contact-set ground is connected to conductor I020 and, through thebottom outer contacts of relay I002, to conductor I020, both of whichconductors provide locking paths to the various relays shown in Figs. 5and 9, as explained hereinafter; (5) over its No. 5 contact-set, groundis connected to conductor I02I which, over the right middle contacts ofrelay 9| I, extends as conductor M4 to resistance II32, contacts ofrelay II2I, left winding of relay I I2I to battery and ground. Relay II2I operates over this self-interrupted circuit and induces currents ateach interruption in the closed inductive path extending from groundthrough the right winding of relay II2I, right winding of coil II3I toground. Inasmuch as the left winding of said coil comprises an elementin the circuit of relays I M2 and IOI3, which circuit extends over thesubscribers loop, said interruptions are repeated over said loop as dialtone which is heard by the subscriber as an instruction that he mayproceed to dial the wanted number; (6) over the No. 6 contact-set ofrelay I0I5 a circuit is completed over the left outer contacts of relayI009 and conductor I 023 through the left winding of relay I I00 tobattery and ground, which relay functions are described hereinafter; (7)over its No. I contact-set, relay I0I5 closes a partial path for relayIOII which extends from battery through the winding of said relay,conductor I022, right outer contacts of relay III I, conductor 9I3, No.I contact-set of relay I0I5 normal contacts of relay IOII to conductorI02I. The manner in which conductor I02I is completed to ground willbecome evident hereinafter from a consideration of the operation of themiscellaneous signaling circuits in Fig. 11, which begins to function assoon as relay I I00 operates at the time ground is connected toconductor I023; (8) over its No. 8 contact-set, relay I0I5 opens thepreviously described circuit of relay I008, causing said relay torelease. In releasing, relay I008 disconnects ground from conductors 3I2and 3I3 and, since the holding magnet 300 is now locked through itslower winding, ground on these respective conductors is no longernecessary while over its left contacts relay I008 completes a circuitfor the link make-busy relay H0 which extends from grounded batterythrough the right winding of said relay, conductor I08, left contacts ofrelay I008, No. 2 contact-set of relay I0I5 to ground. Relay H0 is nowheld operated as long as the link is busy.

Relay II00, on operating, looks over the right winding and right innercontacts to ground on conductor 9M, causes ground to be connected tolocking conductor I I33 which extends to various parts of the circuit ofFig. 11, and further completes a circuit for relay Hill which extendsfrom. ground on the left outer contacts of relay H00, contacts of relayII03, winding of relay IIOI to battery and ground. Relay IIOI operatesand closes an obvious circuit for relay II02 which causes it to operateand to further close an obvious circuit for relay H03. Relay II02further completes a circuit for relay II I6 extending from groundthrough its right contacts, conductor I I38, normal contacts of relay II I6, winding of relay III6, resistance H34 to battery and, in paralleltherewith through the left outer back contacts of relay III5, resistanceH35 to battery. It will be observed that the winding of relay III5 isshort-circuited by the operating ground for relay III6 by the connectionof said ground to one side of its winding at its left outer backcontacts and to the other side of its winding at the normal contacts ofrelay III6. Relay III6 operates, locks to ground on conductor H33 .ofrelay IH5 through its front contacts.

In the meanwhile, the operation of relay H03 opens the circuit of relayIIIlI which, after an interval, releases, in turn opening the circuit ofrelay H02 which releases after an interval and in turn, opening thecircuit of relay H03 which also releases after an interval andreestablishes the circuit for relay HOI to repeat the cycle ofoperations ofrelays HOI, H02 and H03. Relay H02, on releasing, furtherdisconnects ground from the left terminal of relay III5 at the leftouter back contact of said relay, after which said relay operates in acircuit which extends from ground and battery, resistance H35, windingof relay Hi5, front contacts of relay HIE to ground on conductor H33.Relay IH5 operates and establishes a circuit for relay IIII extendingfrom ground on its right outer contacts, left inner normal contacts ofrelay III'I, winding of relay I I I1, resistance I I3! to battery andground. Relay HIT operates and establishes a short circuit for thewinding of relay HM by connecting ground on conductor H33 through itsleft inner contacts to the left terminal of the winding of said relay,ground having been already connected to its other terminal in a pathextending from ground on the right outer contacts of relay HI5, rightouter back contacts of relay IIM to the right side of its winding.

On the next operation of relay H02 ground is again connected toconductor II 38 and since relay I I I5 is operated, said ground isextended to resistance H34 thereby short-circuiting relay I I I andcausing it to release. Relay I I I5, however, does not release since itis now held in an operated position by the ground on conductor H38extended through the normal contacts of relay HIE. On the subsequentrelease of relay H02 and the removal of ground from conductor H38, relayIH releases, the short-circuiting ground for relay HM is disconnectedand this relay now operates in a circuit extending from ground andbattery through resistance H36, winding of relay I I I4, left innercontacts of relay III] to ground on conductor H33.

Upon the next operation of relay H02, relay IH6 operates again over apreviously described path, locks as before and again shortcircuits thewinding of relay HI5. When relay releases, relay III5 operates inparallel with relay HIS and establishes a short circuit for relay III'Iwhich circuit may be traced from ground on the right outer contacts ofrelay II I5, right front contacts of relay HM, resistance H31. RelayIII'I releases and completes a circuit for relay HI8 which may be tracedfrom ground and battery, resistance H40, winding of relay IH8, leftinner normal contacts of relay III8, left middle contacts of relay HI'I,left inner front contacts of relay IIM to ground.

Relay III8 operates and establishes a short circuit for relay H3 byconnecting ground on conductor I I33 through its left inner frontcontacts to the left terminal of the winding of relay I I I3 whileground is connected to the right terminal of its winding through its ownright back contacts, through the left middle contacts of relay III! asalready traced.

When relay H02 operates again, relay HIS releases in the manner alreadydescribed and, when it releases, relay III5 also releases. Inasmuch asrelay HM is held through the normal contacts of relay HH and the rightouter contacts of relay III5, then, with the release of relay HI5, relayIIM'releases. Further, since the winding of relay III3 is heldshort-circuited by ground through its right back contact and extendingover a previously traced path to. the left inner front contacts of relayI I M, then, when said relay releases, the short circuit is removed andrelay III3 operates over a circuit which extends from grounded battery,resistance IM'I, left inner front contacts of relay I I I8 to ground onconductor H33.

Thus, after relay H02 has operated and released four consecutive times,relays III3 and III8 are operated and locked while the two previouspairs of counting relays, namely HI5 and HI6, HM and HH are released.

In the same Way it can be shown that after eight consecutive operationsand releases of relay H02, relays III2 and HI9 will be operated andlocked; that after twelve consecutive operations, relays I I i0 and H20will be operated and locked, that after twenty-four consecutiveoperations, relays H09 and H05 will be operated and locked, and thatafter forty-eight consecutive operations relays H09 and H05 will bereleased. In all cases, all preceding pairs of counting relays will bereleased.

Thus in the circuit of Fig. 11, six pairs of counting relays areprovided which function to count time through the operating cycle ofrelays IIOI, H02 and H03, which cycle can be made as long or as short asdesired by appropriate means. During the interval that a link isconnected to the calling line the counting relay circuit of Fig. 11provides the proper intervals for giving the appropriate signals usuallygiven when calls are not completed in a given length of time and furtherprovides for operating the five ringing relays .I I22-I I26,.inclusive,in the proper interval called for by the ringing code of each of fivestations located on each of the line conductors. Inasmuch as coderinging is well established in the art and can be carried out by anyWell-known means which provides for the closure of the ringing circuitpath in accordance with the code called for by the Wanted station, it isnot thought necessary tounduly lengthen this specification by thedetailed description of all the functions of the circuit shown in Fig.11 except in so far as they are necessary to. a complete disclosure andunderstanding of the operation of the link circuit and the manner inwhich it is used to establish a talking connection between two stations.

Returning, now, to the operation of the link circuit and the fact thatthe calling station has been given dial tone, let it be assumed that thesubscriber does not dial for the time interval measured from the instantrelay H02 operates to the time that relay II I0 operates. If the linkhas not released during this interval, which means among other things,that the subscriber has not dialed, a circuit is completed over apreviously described path to conductor I02I and thence over the innerright back contact of relay H20 and the left front contact of relay HIOas soon as the timing circuit hasadvanced to operate relay HIO. RelayIOH operates, locks over conductor I022, outer back contact of relay 9II, conductor 9I3, No. 1 contacts of relay I0I5 to ground at its leftfront contacts and, over its right contacts, extends the winding ofrelay IOI0 to conductor I024. When the timing circuit has advanced, inthe manner previously described, to the point where relay H09 isoperated and relay H05 is released, ground is connected to conductorI024 over a path which extends through the left front contacts of relayH09 and right contacts of relay II05, causing the operation of relayIOI0 which locks to ground over conductor I022, right outer contacts ofrelay 9! I, conductor 9I3, No. I contact-set of relay I0I5 left contactsof relay IOI I, ground. Relay IOI0 disconnects ground from conductor 3I5over which holding magnet 300 has locked. Magnet 300 releases and freesthe subscribers line at the cross-bar contact-set 3I4. The restorationof the link equipment to normal thereafter is the same as that whichwill be described subsequently for the disconnection of a completedconnection.

Now if the subscriber 024 still has his receiver off the hook after thelink is freed, or if the line is crossed, the line relay 600 willreoperate over the line loop since, with the release of the crossbarpoint, ground is disconnected from conductor 6 I2 causing the cut-offrelay 60I to release, thereby again connecting relay 600 over the line.Relay 602 being slow-release, does not release immediately and before itcan release, the reoperation of relay 600 will cause it to remainlocked, which condition will prevent the reconnection of the ground toconductor 609 and thereby prevent the seizure of another link during thetime that the line is locked out of service.

Assuming, however, that the subscriber does not delay dialing until theoperation of relay I0l0 but that, on hearing dial tone, proceeds to dialthe tens digit 3, then on the interruption of the line which follows thefirst pulse, relays IOI2 and IOI3 release, but relay IOI4, being slow torelease, remains operated during pulse interruptions. A circuit,therefore, is completed which extends from ground on the left backcontacts of relay IOI3, left inner contacts of relay IOI4, conductorI025, winding of relay 905 to battery and ground. Relay 905 operates andcloses an obvious circuit for relay 904 which also operates. Anothercircuit is also completed which extends from ground through the No. 4contact-set of relay I0I5 conductor I020, lower back contacts of relayI002, conductor I026, backcontact of No. 4 contact-set I of relay 9I0,conductor 9I6, right back contacts of relay IOI3, conductor I021, leftback contacts of relay I, contacts of relay 902, winding of relay 903 tobattery and ground. Relay 903 operates and the ground through the leftback contacts of relay 90I is now extended through the left innercontacts of relay 903 to one side of the right winding of relay 90I, theother side of which is also connected to ground through the left frontcontacts of relay 994. Relay 903 further completes a circuit for relay50I which extends from ground through the right front contacts of relay903, left back contacts of relay 900, conductor 9I'I, winding of relay50I to battery and ground. Relay 50I operates but performs no usefulfunction at this time.

When relay IOI3 reoperates on the closure of the line after theinterruption thereof by the first pulse, the circuit which caused theoperation of relay 903 is opened while neither relays 905 nor 904release during the pulse interruption since both of them have slowreleasing characteristics. Moreover, and due to the fact that relay 904does not release, relay 903 does not release either, but holds in acircuit which extends from ground through the left front contacts ofrelay 904, right winding of relay 90!, left inner contacts of relay 903,contacts of relay 902, winding of relay 903 to battery and ground. Relay90I operates in this locking circuit and, on operating, extends groundto conductor 9 I8 which looks relay 50I through its top inner contacts,closes an obvious circuit for relay 900 through the left winding of saidrelay, causing the operation of said relay which further locks over itsright winding and right outer contact to ground on the left frontcontacts of relay 904.

When the line is opened again by the interruption of the second pulseand relay IOI3 consequently releases, the ground previously tracedthrough the right back contacts of relay I 0I3, left armature of relay90I to conductor I021, is now extended over the left front contacts andleft winding of relay 90I, winding of relay 902 to battery and ground,causing relay 902 to operate,

whereupon relay 903 releases and relays 90I and j 902 hold in thecircuit of relay 902 just traced. With relay 993 released, a circuit iscompleted for relay 502 which extends from ground on the right backcontacts of relay 903, conductor 9I9, top outer contacts of relay 50I,winding of relay 502 to battery and ground. Relay 592 operates andcompletes I a circuit which extends from ground through the right outerfront contacts of relay 905, conductor 92!, top outer contacts of relay502, conductor 5I9, normal contacts of relay 909, winding of relay 909,resistance 922, to battery and ground. Relay 909 operates while relay908 remains short-circuited by ground on the battery side of its windingextended thereto over conductor 5I9. On the reoperation of relay !0I3following the closure of the line on the termination of the secondpulse, the holding circuit for relays SM and 902 is opened causing saidrelays to release, but relay 900 being locked to ground on the contactsof relay 904, which relay does not release during the transmission ofthe pulses of a digit, remains locked, whereupon relay 50I is releasedby the opening of the contacts of relay SM and relay 502 is locked in acircuit which extends from ground and battery through the winding ofrelay 502, top inner contacts of said relay, conductor 5I8, left outerback contacts of relay 903, right inner contacts of relay 900 to groundon the left front contacts of relay 904.

On the release of relay I9I3 when the line is opened by the interruptionof the third pulse, relay 903 operates again as it did for theinterruption of the first pulse, and since relay 900 is operated at thistime, a circuit is completed for relay 503 which extends from groundthrough the right front contacts of relay 903, left front contacts ofrelay 900, conductor 920, top middle contacts of relay 502, winding ofrelay 503 to battery and ground. Relay 503 operates. On the reoperationof the relay IOI 3 when the line is closed after the third pulse, relay90I operates while relay 992 does not as before described. However,since the third pulse is the last of the series of pulses for the firstdigit 3, no more pulses will be forthcoming for the interval required bythe subscriber to wind up the dial, an interval sufficiently long tocause the release of relays 904 and 905. However, due to the operationof relay 9! prior to the release of relays 905 and 904, relay 502 isreleased, whereupon the short circuit to the battery side of the windingof relay 903 is removed and this relay now operates in parallel withrelay 909 in a circuit which extends from ground and battery throughresistance 924, winding of relay 908, front contacts of relay 009, toground on conductor 923. When relay 908 operates and, as soon thereafteras relay 905 releases, a circuit is completed for relay 906 whichextends from ground and battery through the left winding of relay 9%,left front contacts of relay 908 to ground on the right outer backcontacts of relay 905. Relay 906 o-p-. crates and locks over'its rightwinding and right inner contacts. to ground on conductor 923. Now, dueto the operation of relay 905 and the prior release of relay 905, relay503 does not release because of a holding circuit which extends frombattery through its winding and top inner contacts, conductor 520, leftouter contacts of relay 995, left inner contacts of relay 996, conductor925, bottom outer contacts of each of the relays 5H3, BIZ and 5| I, toground. A circuitis now completed for relay 5I2 which extends fromground on the left back contacts of relay 996, right middle contacts ofrelay 906, right outer back contacts of relay 90'I, conductor 92%,bottom middle con tacts of relay 503, top winding of relay 5B2, tobattery and ground. Relay 5I2 operates over its top winding and locksoverits lower winding and bottom inner contacts to ground on conductor923. The operation of relay 5I2 registers the tens digit 3 and unlocksrelay 593 which releases.

The subscriber now dials the second or units digit which, under ourassumption is the digit 1. When relay I I it releases on the lineinterruption, relays 904 and 905 operate as before described and thepreviously traced pulsing ground causes the operation of relay 903,after which a previously described circuit path is completed foroperating relay 50I which further looks over conductor 9! to ground onthe right middle contacts of relay 90L When relay 995 operates at thebeginning of the pulse a shunting circuit is completed for relay909-which extends from ground on the right outer front contacts of relay905, left outer contacts of relay 99%, right front contacts of relay909, to resistance 922. Relay 909 releases but relay 903 continues tohold through the right normal contacts of relay 909 to ground, astraced, on the right outer front con tacts of relay 995. On thereoperation of relay IOI3, at the termination of the pulse, relay 99ioperates in series with relay 903 followed by the operation of relay 909and, after an interval, relays 905 and. 994 release, causing the releaseof relays Bill and 903 after which relay re leases. Further, with therelease of relay 995, the

holding circuit for relay- 909 is broken and this relay releases.Thereupon, a circuit is completed for relay 901 which extends fromground and battery through the winding of said relay, right outercontacts of relay 909, left back contacts of re lay 908, right outerback contacts of relay 935 to ground. Relay 9-01 operates and locks toground on conductor 923.

Now if the units digit of the wanted subscribers number had been anyother digit than the digit 1, say the digit 6, then six pulses wouldhave been dialed and would have resulted in the opera tion of relay 506by circuit operations similar to those described for the hundreds digit3. When,-

in this assumed series of six pulses, relay 55 2 crates on the secondpulse, ground is connected to resistance 922 over a path extending fromthe right outer front contacts of relay 905, conductor 92!, top outercontacts of relay 592, conductor 5l9, right front contacts. of relay 908to resistance 922. This causes relay 999 to be shunted and released,causing relay 908 to be held locally so long as relay 905 remainsoperated; that is, until all the six pulses of the digit are received,at which time it releases and completes the operating circuit of relay901, already described. A circuit is now completed for relay 5M whichextends from ground and battery through the lower winding of relay 5M,No. 3 contact-set of other frames as required.

relay 506, conductor 52I, No. I contact-set of relay 9I0, right outerfront contacts. of relay 991, right middle contacts of relay 900 toground on the left back contacts of relay 994. Another circuit is alsocompleted for relay 5i 5 which extends from ground and battery throughthe lower winding of relay 5I5, No. 0 contact-set of. relay 5% to groundas traced on conductor 52%. Both of these relays operate and then lookover their re spective top windings. and top inner contacts to ground onconductor 923.

The reason why, in the case of any units digit higher than 1, it isnecessary to operate one or more of the four relays 5I4-5I'I is the factthat, for each digit including 1, a record of the digit must bepreserved for the future operation of the proper selecting magnet in thelink for reaching the wanted line. Each of the first two digits of theWanted number represents a specific function which must be performed toreach the wanted line. Referring to Fig. 12, it is evident that thefirst, or tens digit, represents the particular link frame on which thewanted line terminates. Since the invention can accommodate a maximum offifty lines with ten lines to the frame, it is obvious that the lines onthe first frame will have a tens digit which will identify the frame,and inasmuch as the digit 1 is not used as the tens digit, all the lineslocated on the first frame will have a digit 2 for the tens digit whilethose on the second frame will have a digit 3. I have chosen toillustrate my invention as adapted to twenty lines, spread over twoframes with an additional split frame to accommodate two more links thatcould not be accommodated on the first two frames, so that the linesterminating on the first frame all have a 2 as a tens digit and thoseterminating on the second frame have a 3 as a tens digit. In othergroups of ten lines each were to be added to the office up to a maxi mumof fifty lines, then each of these groups would have a 4, a 5 and a 6,respectively, as the tens digit.

Hence, so far as the operation of the invention is concerned, the tensdigit is used to identify the frame on which the wanted line is located,and this fact is recorded on the operation of one or more of the threerelays 5 to 5I3, inclusive, by the connection of ground to one of thefive conductors that identify each of the frames accommodating a groupof ten lines. Since the illustration of the operation of the inventionhas been limited to twenty lines, ten on each frame, only two of theseconductors, namely 522 and 523, are used and connected to such parts ofthe circuit as are controlled over these conductors; the remaining threebeing bracketed and labeled to Since, in the call being illustrated, thewanted subscriber is located on the second frame and therefore involvesthe digit 3 as the first digit, the relay operated on the tens digit 3was relay 5I2 to make conductor 523 effective at the proper time.

The relationship between the operation of the relays 5| I--5I2 and eachof the tens digit which ten lines to the frame is as follows:

Digit Relays operated The seconds or units digit of the subscribers lineis that which identifies the horizontal level in the frame on which theline terminates, and this fact is recorded in the four register relays5I4 to 5H, inclusive, in order to eventually prepare a circuit foroperating the horizontal magnet involved for reaching the wanted line.These relays are operated or non-operated in particular combinations bythe operated relay in the group of relays 50I to 5I0 which is responsiveto the digit dialed. In the case of the call being used to illustratethe operation of the invention and which has the digit 1 as its unitsdigit, none of these relays was operated following the operation ofrelay 50I. If the wanted line had had the digit 6, as assumed fordetailing the function of relays 5 to 5I'I, then relays 5M and 5I5 wouldhave been operated as described. The relationship between the unitsdigit dialed and the relays operated is as follows:

Digit Relays operated Returning, now, to the number being dialed bystation 624; that is number 3I9, and remembering that the dialing of theunits digit 1 resulted in the non-operation of the relays 5M to 5, aswell as the release of relays 908 and 909 and also the release of relay50I, the subscriber is now ready to dial the last or the ringing digit9. Each of the pulses of the digit causes the operation of relays 900,MI, 902 and 903 in the manner described, followed by the successiveoperation and release of relays 50I-509. It will be recalled, however,that during the dialing of the units digit and as a result of theoperation of relay 905 at the beginning of the digit and its release atthe end of the digit, relays 908 and 909 were released. However, whenthe second pulse has been received and relay 502 has operated inconsequence, a previously described circuit path is closed for relay909, causing said relay to operate. When relay 502 releases, relay 908is operated in parallel with relay 909, as before described. On theninth or last pulse, relay 509 is operated and held over its lockingcontacts to ground on conductor 520 so long as the pulsing relay 903remains operated. However, at termination of the pulse, the release ofrelay 905 causes a circuit to be closed extending from ground throughthe right outer back contacts of relay 905, left front contacts of relay908, left outer contacts of relay 901, left winding of relay 9I0 tobattery and ground. Relay 9I0 operates, locks over its right winding andNo. 4 front contacts, conductor I026, bottom outer contacts of relayI002 to ground on the No. 4 contact-set of relay II5 and extends groundover its No. 5 contacts to the right winding of relay 90I, causing thepulsing relays 900, 90I, 902 and 903 to hold after the release of relay904 following the termination of the last pulse of the ringing digit.With relays 903 and 900 remaining operated, relay 509, instead ofreleasing as it would have done if it had operated on a 9 units digit,remains locked to ground on the N0. 5 contacts of relay 9I0. Relay 9I0further causes relay 904 to be held over its No. 8 contact-set to groundon conductor 923 in preparation for making the busy test of the wantedline as explained hereinafter.

The operation of relay 9I0 further causes a circuit to be completedwhich extends from ground on the left outer back contacts of relay 9| I,No 2 contacts of relay 9I0, conductor 928, right winding of relay I00'Iconductor I028, left contacts of relay I03, right back contacts of relayI02, battery and ground. Relay I00! operates and completes a lockingpath extending from ground on conductor 928, left winding of relay I00'Iand left inner front contacts, conductor I029, Winding of relay I03,right back contacts of relay I02, to battery and ground. Relay I03operates in this locking circuit, opens the operating circuit of relayI00! at the left contacts of relay I03 and also the operating circuit ofrelay I001 in every link. The locking circuit of each of said relays islikewise opened by the operation of relay I00'I since said lockingcircuit is controlled over conductor I030 which extends over the backcontacts of each of relays I001 in a chain arrangement, so that oncerelay I001 of one link is locked, corresponding relays in other linkscannot operate, thereby looking out other links which may be seekingaccess to the frame containing the wanted line.

Relay I00'I on operating, closes an obvious circuit for relay I006which, on operating, causes a circuit to be completed for relay 9IIextending from ground through the right outer contacts of relay I906,conductor I03I, winding of relay 9| I, to battery and ground. Relay 9operates and looks over its right inner front contacts to ground onconductor I020. In the meanwhile, the operation of relay I001 causes theconnection of ground to conductor I032 which extends to the top armatureof relay 5. Inasmuch as relay 5I2 has been operated for the tens digit3, said ground is extended to complete a circuit over the top backcontact of relay 5II, top outer front contacts of relay 5l2, top innerback contacts of relay 5I3, conductor 523, winding of relay 605 tobattery and ground; winding of relay 604 to battery and ground andwinding of relay 603 to battery and ground. Relay 603 operates and opensthe path of each horizontal selecting magnet on the second frame, eachof which extends back to a corresponding line relay of a subscribersline on this frame; relay 604 operates and extends the operating windingof each of said magnets to each of the ten conductors extending to thecontacts of relays 5I4-5I1, while relay 505, over its left frontcontacts, connects ground and battery to each of the operating windingsof said horizontal magnets while over its right inner contacts itextends ground to conductor 62I which is connected to the operatingwindings of all link holding magnets 10 I -101 Since the units digit ofthe wanted subscribers number is 1, and since the impulse of this digitresulted in the operation and locking of none of the relays in the groupof relays 5I4-5Il inclusive, a circuit is completed which extends fromground on the right inner contacts of relay I00'I conductor I033, leftouter contacts of relay 500, bottom outer back contacts of relays5I4-5II inclusive, conductor 524, No. I contacts of relay 604, rightwinding of horizontal selecting magnet 601, left contacts of relay 605,to battery and ground. Magnet 60! operates and prepares the horizontalcross-points for contact with the vertical at the link attached to thecrosspoint of the calling line. In the meanwhile, the

ground connected to conductor 62I completes a II circuit through the topwinding of. holdingmage net llll of the first link, conductor. 102, leftcontacts of relay I006 to battery and ground. Hold: ing magnet 'I0Ioperates over its top winding and then looks over its lower winding andcontacts in a previously described circuit. Since the circuit ofhorizontal selecting magnet 601. was closed ahead of that of holdingmagnet 'I0I by the fact that the former circuit is completed by relay1001 and that of the latter by relay lime which is slow-operate, thecross point contacts controlled by magnet 601 are set for lockingundercontrol of magnet 'I0I in advance of the opera tion of said magnet, asrequired for the proper operation of across-bar switch. a

When relay 9H operatesit opens the circuit of relay I'I which, onreleasing, further releases relay I000 disconnects ground from conductor023 which latter causes the release of all relays locked to saidconductor including relay 904, connects ground to conductor IOI8 whichextends to the winding of relay [M3 to replace ground supplied fromconductor 9I5, andif the wanted line is idle after testing it in themanner to be described hereinafter completesa circuit which extends fromground through the i left inner back contacts of re1ay500, conductor525,

left middle contacts of relay 9| I right outer con tacts of relay 904,conductor 929, right outer contacts of relay I009, winding of relayI005, to battery and ground. l V

.If the wanted line'is busy, relay 6I4 of said line is operated and assoon as cross-point, I03 is operated and before relay 9| I shall havehad time to operate and, therefore, remove ground from conductor 923,,apath is completedfor relay I000v which extends from ground. and batterythrough the winding of said relay, conductor I045, right inner contactsof relay 904, conductor I039, third contact of cross-point I03,conductor 625, right outer front contacts of relay 6 I4 to ground. RelayI009 operates, locks to ground onthe No. 3 contact-set of relay IllI5under the control of the bottom inner back contacts of relay IO0I, cutsoff the operating circuit of relay I005, opens the circuit of relay II00 which, however, does not release at this time because it is held upover another ground to its right winding extending over conductor II43,bottom inner contacts of relay i005, No. 1 front contacts of relay I009,to ground through the No. fi contacts ofrelay I0I5 and completes a busytone circuit for the calling line which extends from ground through theright winding of inductioncoil I:I3I, left inner front contacts of relayIII5, condenser H44, conductorv H46, No. 6 contacts of relay I009, topouter back contacts of relay I005, top outer back contacts of re1ayl004,upper winding of relay I002, to ground and,-in parallel therewiththrough condenser I044, bottom outer con tacts of relay IO0I, bottomouter back contactsof relay I000, conductor IOI'I, second contact ofcross-point 3I4, conductor BI I, subscribers loop 624, conductor 609,first contact of cross-point 3I4, conductor 3I6, top outerback contactsof relay I000, top outer contacts of relay IO0I, condenser I034, lowerwinding of relay I002 to battery and ground and, in parallel therewith,bottom back contacts of relay I004, bottom outer back contacts of relayI005, No. 5 contacts of relay I009,conductor H41, condenser H45, rightinner contacts of relay I I I5 to ground. The subscriber hears thetonewhich isinterrupted at regular intervals by the operationand release ofrelay? I I I5 asbeforedescribed. He is by this means notified that thecalled line is busy and restores his receiver to the switchhook.

If the, wanted line is not busy, relay GM is normal, relay I009 does notoperate and the circuit of relay I005 is completed as before described.Relay I005 operates and looks over its operating path to ground onconductor .929. It further completes a circuit for operating the calledline cut-off relay 6I3 which extends from ground through the bottommiddle contacts of relay I005, conductor I039, fourth contact ofcross-point J03, conductor 025, right outer back contacts of relay 6I4,winding of cut-off relay M3 to battery and ground. Relay 6I3 operates,removes the line relay 6I2 from the line and prevents the subscriberfrom initiating a call.

As soon as relay I005 is operated, the wanted line is out throughtto thecalling line preparatory to the closure of the ringing circuit over apath hereinafter described.

It will be recalled that, when the link is seized, the alarm circuitshown in Fig. 11 begins to function as soon as ground is connected toconductor I023, and that the pairs of counting relays like relay I I I5and IIIO operate and release to count off time in the manner described.As soon as relay III'I operates, ground is connected to conductor H39through the left middle back contacts of relay I I I9, right middle backcontacts of relay III8, right inner front contacts of relay III'I toconductor H39 which further extends through theright middle backcontacts of relay I009, top inner continuity contacts of relay I004,conductor I036, left inner contacts of relay 9| I, conductor 930,conductor I031, winding of relay I004 to battery and ground. Relay I004operates and looks over its top inner front contacts, conductor I038, toground through the left outer back contacts of relay III2 which isnormal at this time.

During the period in which relay I004 is operated, the calledsubscribers station is being rung, and this period is measured from thefirst release of relay H02 to the operation of relay IlI2 on the eighthconsecutive release of relay H02, as already described.

The operation of relay I 004 completes the ringing circuit to the calledsubscribers line and in theproper ringing code combination determined bythe last digit of the wanted number which, in this case, is determinedby the digit 9 and, therefore, by the operation of relay 509. Inasmuchas the operation of the invention is being disclosed with respect to arural exchange having five stations on the tip conductor of the line andfive stations on the ring conductor, the different stations must be rungby a code individual to each station although the invention is notlimited to a plurality of stations on one line or even to a singlestation. Under these circumstances, relays I I23 to H26 each provide adifferent ringing code for each of the five stations on one of the lineconductors and the circuit for operating each of 1 said relays iscontrolled in the appropriate order and for the required length of timeby the pairs of counting relays shown in Fig. 11. Inasmuch as this partof the circuit is ancillary to the operation of the invention in thatringing code relays and the manner of their control are well establishedin the art, it is not deemed necessary to describe the various operatingcircuits for the relays H23 to H26 except to mention the fact that relayII22 provides a code of two medium rings per cycle; relay H23 threeshort rings; relay H24 four short rings; relay

